In order to keep the technology competitive for a much longer time period, both third generation partnership project (3GPP) and 3GPP2 are considering long term evolution (LTE), in which evolution of radio interface and network architecture are necessary.
Currently, LTE specifies that uplink transmissions are to be based on single carrier-frequency division multiple access (SC-FDMA). One method for generating an SC-FDMA signal is to use a discrete Fourier transform (DFT) spread Orthogonal Frequency Division Multiple Access (OFDMA) processing. An N-size DFT is applied to a block of N modulation symbols, transforming the modulation symbols into the frequency domain. The result of the DFT is mapped onto the available subcarriers.
For the mapping, a basic scheduling unit in LTE is a resource block (RB), where uplink data is allocated to each WTRU in multiples of RBs. One RB typically consists of 12 subcarriers in the frequency domain. For wireless communications using a 20 MHz bandwidth, the channel is typically divided into 1200 subcarriers with 100 RBs available. As each wireless transmit/receive unit (WTRU) may have any number of RBs assigned to it for uplink transmission, the following constraints arise.
For a UE with N subcarriers (that is N/12 RBs) allocated in the uplink, a DFT precoding with a size of N will be applied, where N can be decomposed as the product of M prime factors' power and defined by the following equation:
                    N        =                              ∏                          i              =              1                        M                    ⁢                                          ⁢                                    K              i                              L                i                                      .                                              Equation        ⁢                                  ⁢        1            In Equation 1 above, M represents the number of prime factors, K1, K2, . . . , KM are prime factors and L1, L2, . . . , LM are the corresponding powers.The number of required complex multiplications, denoted by NDFT, is given by the following equation:
                              ND          ⁢                                          ⁢          F          ⁢                                          ⁢          T                =                  N          ⁢                                    ∑                              i                =                1                            M                        ⁢                                                  ⁢                                          K                i                            ⁢                                                L                  i                                .                                                                        Equation        ⁢                                  ⁢        2            Since a DFT precoding size N with large prime number factors causes very high transmitter implementation complexity, it is preferable to limit N to an integer that has only prime factors of 2, 3 and 5.
Secondly, in order to represent all integer numbers of RBs from 1 (or 0) to N/12, an n-bit mapping (n=┌log2(N/12)┐) is required if full resolution is used. In a LTE with 20 MHz, there are 100 available RBs. Therefore, a 7-bit mapping is required (i.e., 26<100<27) if full resolution is used. However, 7 bits results in a relatively large overhead for a scheduling request by the WTRU and an uplink scheduling grant by the network.
In order to support a variety of uplink data rates with low transmitter complexity and low signaling overhead, a method is needed to reduce overhead in uplink scheduling grant mapping and uplink scheduling request signaling.